/St. Louis Encephalitis (SLE)

St. Louis Encephalitis (SLE)

What is SLE?

SLE is a potentially serious viral disease that affects humans, birds, mosquitoes and other animals.

Who gets SLE?

Anyone living in an area where virus activity has been identified is at potential risk of infection.

Is SLE in Clark County?

Although not as common as West Nile virus, the Vector Control program has identified SLE in Clark County mosquito pools and several human cases have been reported.

How does SLE spread?

SLE is most often spread by the bite of an infected mosquito. Mosquitoes (SLE carriers) become infected when they feed on infected birds (SLE reservoirs).

Infected mosquitoes can then spread SLE to humans and other animals when they bite. SLE is not spread from person-to-person.

What are the symptoms of SLE?

Most people who are infected with SLE have very mild illness or may never become sick. Mild infections are characterized by fever and headache, without other apparent symptoms.

The symptoms of severe disease can include:

  • headache
  • high fever
  • neck stiffness
  • confusion
  • coma
  • shaking
  • seizures and/or paralysis

The risk of severe disease increases in older people.

How soon do infected people get sick?

People typically develop symptoms between five and 15 days after they are bitten by infected mosquitoes.

How is SLE diagnosed in humans?

SLE is diagnosed by laboratory confirmation that the virus is present in a person’s blood sample.

How is SLE in humans treated?

There is no specific treatment for SLE infection. Cases with milder symptoms resolve on their own.

In more severe cases, people usually need to go to the hospital to receive treatment.

How can SLE infection be prevented?

The easiest and best way to avoid SLE is to prevent mosquito bites:

  • When outdoors, follow the directions for using an insect repellent registered by the Environmental Protection Agency (EPA), such as those containing:
    • DEET (N, N-diethyl-meta-toluamide)
    • Oil of lemon eucalyptus
    • Picaridin
    • Permethrin
  • Wear pants and long-sleeved shirts when outdoors.
  • Avoid spending time outside when mosquitoes are most active, notably at dusk (the first two hours after sunset) and dawn.
  • Eliminate areas of standing water, including bird baths and un-maintained swimming pools, which support mosquito breeding.
  • Make sure doors and windows have tight-fitting screens without tears or holes.

There is a vaccine to prevent infection in horses, but no vaccine for humans.

How is SLE being addressed in Clark County?

The health district’s Environmental Health Division, in collaboration with the Nevada Division of Public and Behavioral Health, conducts surveillance to monitor mosquitoes for SLE.

Where can I get more information?

Contact your doctor or the Southern Nevada Health District Office of Epidemiology at (702) 759-1300. You may also visit the CDC’s website at http://www.cdc.gov/sle/.

Contact Information

(702) 759-1300

(702) 759-1220

Updated on: February 27, 2019

Skip to content